1. Field of the Invention
Aspects of the present invention relate to an organic light emitting diode (OLED) display device and a method of fabricating the same, and more particularly, to an OLED display device including a capacitor whose capacitance is increased using a method of fabricating a polysilicon layer using a metal catalyst and a method of fabricating the same.
2. Description of the Related Art
In general, polysilicon is widely used as a semiconductor layer of a thin film transistor due to its high field effect mobility and applicability to high-speed operating circuits and complementary metal-oxide-semiconductor (CMOS) circuits. The thin film transistors having a polysilicon layer are generally used as active elements of active matrix liquid crystal displays (AMLCDs), and switching elements and driving elements of organic light emitting diodes (OLEDs).
Here, methods of crystallizing an amorphous silicon layer into the polysilicon layer used for a thin film transistor include a solid phase crystallization (SPC) method, an excimer laser crystallization (ELC) method, a metal induced crystallization (MIC) method, and a metal induced lateral crystallization (MILC) method. In the SPC method, an amorphous silicon layer is annealed at a temperature of about 700° C. or less, i.e., a transition temperature of a glass substrate of a display device for several hours to several tens of hours. In the ELC method, an excimer laser is irradiated on an amorphous silicon layer to locally heat the irradiated portion to a high temperature for a very short time period, so that the amorphous silicon layer is crystallized. In the MIC method, metals such as nickel, palladium, gold, aluminum, etc., are placed in contact with or injected into an amorphous silicon layer, so that the amorphous silicon layer is changed into a polysilicon layer, i.e., a phase change of the amorphous silicon is induced by the metal. In the MILC method, silicide, which is produced by reacting metal with silicon, is laterally and continuously diffused to sequentially induce crystallization of the amorphous silicon layer.
However, the SPC method requires a long time, and the annealing process is performed at a high temperature for a long time, which may deform a substrate. Also, in the ELC method, a high-priced laser device is required, and protrusions may be formed on the polycrystalline surface such that interfacial characteristics between a semiconductor layer and a gate insulating layer may deteriorate.
Currently, research into methods of crystallizing an amorphous silicon layer using a metal is actively progressing because crystallization can be achieved at a lower temperature and with less time than the SPC method. The methods of crystallizing an amorphous silicon layer using a metal include the MIC method, the MILC method, and a super grain silicon crystallization method.
Meanwhile, in an OLED, capacitors are formed, and a capacitor having a high capacitance may be advantageous to the operation of the OLED. Thus, research into increasing the capacitance of the capacitor is required.